The long-term objective is to identify the cellular and molecular mechanisms responsible for cerebrospinal fluid (CSF) secretion and the maintenance of the blood-CSF barrier. In vitro preparations of the choroid plexus will be used to study i) the secretion of the CSF, ii) the transport of solutes (amino acids) across the blood-CSF barrier, iii) the control of these processes by hormones and neurotransmitters. Electrophysiological techniques including, ion-specific microelectrodes and patch-clamp recordings will be utilized to define the transport properties of the intact epithelium and membrane patches. Biochemical and biophysical techniques will be used to identify and characterize specific transport processes in isolated plasma membrane vesicles. In particular, fluorescent probes will be used to label specific membrane proteins, and the functional topology of these proteins will be measured by energy transfer and quenching techniques. During this phase of this long-standing project, two very specific questions will be addressed: the first is to test our hypothesis that brush border HCO-3 channels are involved in the regulation of CSF secretion, and the second is to identify and characterize the Imino carrier in brush border membranes. Understandably, the physiology of the blood-CSF barrier has important implications in the clinical management of the central nervous system in such diverse cases as trauma, hydrocephalus, and organic mental disorders. Our studies will pave the way towards therapeutic management of CNS fluid disorders using pharmacological procedures. In addition, our work has unique relevance to basic concepts of transport in neurons and epithelial cells.